Develop Reference

Changing legend text in chart js causing issues

I'm trying to shorten my chart legends, so I'm using the beforeRender plugin to change the text of the legend. However, once the chart is drawn, it seems to keep the original label size (see below snippet, legends are offset to the left instead of in the centre and if you click on orange, it toggles one of the earlier items).
The same happens if I try in beforeDraw and if I use beforeInit or beforeLayout, the legends don't seem to have been created yet.
Is there any way to get the chart to redraw the legends with the new text? Or change the legend text so that it is rendered properly?
var ctx = document.getElementById("canvas").getContext("2d");
window.myBar = new Chart(ctx, {
type: 'pie',
data: {
labels: ['red - some other text that appears after', 'blue - some other text that appears after', 'green - some other text that appears after', 'orange - some other text that appears after'],
datasets: [{
data: [4, 2, 10, 3],
backgroundColor: ['red', 'blue', 'green', 'orange'],
}],
},
options: {
responsive: true,
},
plugins: [{
beforeRender: chart => {
chart.legend.legendItems.forEach(label => {
const labelParts = label.text.split(' - ');
const newLabel = label;
newLabel.text = labelParts[0];
return newLabel;
});
},
}],
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.4/Chart.bundle.js"></script>
<div style="width: 100%">
<canvas id="canvas"></canvas>
</div>

A better approach would be to use a custom generateLabels function like so:
var ctx = document.getElementById("canvas").getContext("2d");
window.myBar = new Chart(ctx, {
type: 'pie',
data: {
labels: ['red - some other text that appears after', 'blue - some other text that appears after', 'green - some other text that appears after', 'orange - some other text that appears after'],
datasets: [{
data: [4, 2, 10, 3],
backgroundColor: ['red', 'blue', 'green', 'orange'],
}],
},
options: {
responsive: true,
legend: {
labels: {
generateLabels: function(chart) {
const data = chart.data;
if (data.labels.length && data.datasets.length) {
return data.labels.map(function(label, i) {
const meta = chart.getDatasetMeta(0);
const style = meta.controller.getStyle(i);
return {
text: label.split(' - ')[0],
fillStyle: style.backgroundColor,
strokeStyle: style.borderColor,
lineWidth: style.borderWidth,
hidden: isNaN(data.datasets[0].data[i]) || meta.data[i].hidden,
// Extra data used for toggling the correct item
index: i
};
});
}
return [];
}
}
}
},
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.4/Chart.bundle.js"></script>
<div style="width: 100%">
<canvas id="canvas"></canvas>
</div>

Counting string to plot a graph using chart.js and angular

I am trying to create a bar chart in angular using chart.js and angular.
I want to display the disaters vs area. with the type of disaster ( earthquake, hurricane, storm...etc) on the x-axis and area (as in location) on the y-axis.
However, the area data is string and does not work when trying to plot a bar graph as it requires numbers.
I am reading the data as follows:
ngOnInit(): void {
this.chartService.noOfEqu().subscribe((res) => {
let area = res.map((res) => res.area);
let disaster = res.map((res) => res.disasterNature);
new Chart('disasterCanvas', {
type: 'bar',
data: {
labels: disaster,
datasets: [
{
data: area,
label: 'area',
backgroundColor: '#A121D5',
},
],
},
options: {
plugins: {
legend: {
display: true,
},
},
scales: {
x: {
ticks: {
display: true,
},
},
y: {
ticks: {
display: true,
},
},
},
},
});
});
}
}
Where let area = res.map((res) => res.area); is the area variable.
I want to know what is the best way to structure the data to be entered into the graph.
The disaster data that is logged is:
and the area data :
How can i structure the area such that it counts how much areas that a disaster has occured and plot it on the bar chart?
Thank you in advance...if there is anything i can clarify please let me know in the comments
Also is there another way to display this data besides tallying the string data?

You need to add a labels array to the scale and set the type to category to use string data:
const options = {
type: 'bar',
data: {
labels: ["Earthquake", "Tornade", "Flood"],
datasets: [{
label: '# of Votes',
data: ['Paris', 'Berlin', 'London'],
backgroundColor: 'pink'
}]
},
options: {
scales: {
y: {
type: 'category',
reverse: true,
labels: ['', 'London', 'Paris', 'Berlin']
}
}
}
}
const ctx = document.getElementById('chartJSContainer').getContext('2d');
new Chart(ctx, options);
<body>
<canvas id="chartJSContainer" width="600" height="400"></canvas>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/3.7.1/chart.js"></script>
</body>

How can I display the xAxes and yAxes data in the tooltip, Chart JS?

I am trying to achieve the Tooltip shown below in the first image. Inside of the tooltip I need to display the yAxes and xAxes data. The chart.js version I am using is 3.7.0
My tooltip looks like this:
The tooltip that I am trying copy:
The chart.js documentation is quite hard for me to understand. Is there any guru that can explain to me.
Question: Why is my tooltip returning the yAxes data, that I return as a variable(label) as undefined?
Are there any other options I can use to make my chart look like the chart in the second picture?
My Code:
tooltip: {
displayColors: false,
backgroundColor: 'rgba(45,132,180,0.8)',
bodyFontColor: 'rgb(255,255,255)',
callbacks: {
title: function(item, everything){
return;
},
label: function(item, everything){
//console.log(item);
//console.log(everything);
let first = item.yLabel;
let second = item.xLabel;
let label = first + ' ppm';
return label;
}
}
}
Thank you in advance for your time and efforts, please help me figure out what am I doing wrong!

yLabel and xLabel dont exist anymore on the tooltip, they are V2 syntax.
You can just axess the y object in the parsed section to get the y value. Then you can use the afterBody callback to show the x label like so:
const options = {
type: 'line',
data: {
labels: ["Red", "Blue", "Yellow", "Green", "Purple", "Orange"],
datasets: [{
label: '# of Votes',
data: [12, 19, 3, 5, 2, 3],
borderColor: 'pink'
}]
},
options: {
plugins: {
tooltip: {
displayColors: false,
backgroundColor: 'rgba(45,132,180,0.8)',
bodyFontColor: 'rgb(255,255,255)',
callbacks: {
title: () => {
return
},
label: (ttItem) => (`${ttItem.parsed.y} ppm`),
afterBody: (ttItems) => (ttItems[0].label)
}
}
}
}
}
const ctx = document.getElementById('chartJSContainer').getContext('2d');
new Chart(ctx, options);
<body>
<canvas id="chartJSContainer" width="600" height="400"></canvas>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/3.7.0/chart.js"></script>
</body>

Chart.js Treemap Custom text

In my code below, I am able to draw a Treemap and also display the tag in each tree cell. But I want to add some custom text next to my tag,
Like say I want the word 'Language' to appear in each tree map cell. I tried the formatter options, But its not working for the version of chart.js I am using. Kindly provide me a solution for the specific version I am using. Since I have multiple other charts defined and changing the version would cause issues.
var topTags = [
{tag:'android',num:42657},{tag:'reactjs',num:38844},{tag:'php',num:34381},{tag:'sql',num:29996},
];
var canvas = document.getElementById("treemap");
var ctx = canvas.getContext("2d");
var chart = window.chart = new Chart(ctx, {
type: "treemap",
data: {
datasets: [{
tree: topTags,
key: "num",
groups: ['tag'],
spacing: 0.5,
borderWidth: 1.5,
fontColor: "black",
borderColor: "grey"
}]
},
options: {
maintainAspectRatio: false,
legend: { display: false },
tooltips: { enabled: false }
}
});
CHART.JS AND TREEMAP VERSION :
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.4/Chart.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/chartjs-chart-treemap#0.2.3"></script>

The formatter option only got added in version 2 of the treemap chart type, the scriptable option is only available in version 1 so the best way for you to get the extra text is by editing your original data array first and adding the text to it that way like so:
let topTags = [{
tag: 'android',
num: 42657
}, {
tag: 'reactjs',
num: 38844
}, {
tag: 'php',
num: 34381
}, {
tag: 'sql',
num: 29996
}, ];
topTags = topTags.map(e => ({
num: e.num,
tag: `Lang: ${e.tag}`
}))
const canvas = document.getElementById("chart");
const ctx = canvas.getContext("2d");
const chart = window.chart = new Chart(ctx, {
type: "treemap",
data: {
datasets: [{
tree: topTags,
key: "num",
groups: ['tag'],
spacing: 0.5,
borderWidth: 1.5,
fontColor: "black",
borderColor: "grey",
}]
},
options: {
maintainAspectRatio: false,
legend: {
display: false
},
tooltips: {
enabled: false
}
}
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.4/Chart.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/chartjs-chart-treemap#0.2.3"></script>
<canvas id="chart"></canvas>

chart.js - how to draw and manage line when only one label present in chart js Linechart

I'm using Chart.JS v 2.9.3 to create a line chart
line-chart diagram to show the month-wise total of expenses of selected product
For example, if the user select XYZ product then this charts would show the monthly expenses [Jan-2021-Dec-2021]
and if that respective product expense only present Jan-2021 then it displays month on y-Axes at staring
here is jsfiddle example
Adding offset trick I had already tried xAxes : [{ offset:true }],
var config = {
type: 'line',
data: {
labels: ["jan-2021"],
datasets: [{
label: "month-year",
data: [65],
backgroundColor: "rgb(118, 101, 228)",
}],
},
scales : {
xAxes : [{
offset:true
}],
},
};
var ctx = document.getElementById("myChart").getContext("2d");
new Chart(ctx, config);
<div class="myChart">
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.3/Chart.bundle.js"></script>
<canvas id="myChart"></canvas>
</div>
please refer to the above image for getting an idea of what I'm trying to archive, I'm not concern about dot that on the chart
As you can see, the points are stick to the y-axis. Is there a possibility to center the line chart when only one data is present in the diagram?

Chart.js does not support this kind of use case since it gives a distorted image of your chart since point and label don't align anymore. If you really want this you can check beforehand in your code if there is only 1 data point there. If this is the case add an empty string in your labels array in the front and back and add zero at the front of back of your data array (or a slightly lower value as your single datapoint so that the scales don't get big steps) like so:
var config = {
type: 'line',
data: {
labels: ["", "January-2021", ""],
datasets: [{
label: "month-year",
data: [0, 134335066, 0],
backgroundColor: "rgb(118, 101, 228)",
}],
},
scales: {},
};
var ctx = document.getElementById("myChart").getContext("2d");
new Chart(ctx, config);
<div class="myChart">
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.4/Chart.bundle.js"></script>
<canvas id="myChart"></canvas>
</div>

You can use align option:
var mybarChart = new Chart(ctx, {
type: 'bar',
responsive: true,
data: data,
options: {
legend: {
display: false,
position: 'bottom',
align: 'center'
},
var config = {
type: 'line',
data: {
labels: ["", "January-2021", ""],
datasets: [{
label: "month-year",
data: [0, 134335066, 0],
backgroundColor: "rgb(118, 101, 228)",
}],
options: {
legend: {
display: false,
position: 'bottom',
align: 'center'
},
},
scales: {},
};
refer to this